use std::char;
use std::collections::{HashMap, HashSet};
use std::num::FromStrRadix;
use std::str;

use {Array, Table, Value, String, Float, Integer, Boolean, Datetime};

pub struct Parser<'a> {
    input: &'a str,
    cur: str::CharOffsets<'a>,
    tables_defined: HashSet<String>,
    pub errors: Vec<Error>,
}

#[deriving(Show)]
pub struct Error {
    pub lo: uint,
    pub hi: uint,
    pub desc: String,
}

impl<'a> Parser<'a> {
    pub fn new(s: &'a str) -> Parser<'a> {
        Parser {
            input: s,
            cur: s.char_indices(),
            errors: Vec::new(),
            tables_defined: HashSet::new(),
        }
    }

    fn next_pos(&self) -> uint {
        self.cur.clone().next().map(|p| p.val0()).unwrap_or(self.input.len())
    }

    fn eat(&mut self, ch: char) -> bool {
        match self.cur.clone().next() {
            Some((_, c)) if c == ch => { self.cur.next(); true }
            Some(_) | None => false,
        }
    }

    fn expect(&mut self, ch: char) -> bool {
        if self.eat(ch) { return true }
        let mut it = self.cur.clone();
        let lo = it.next().map(|p| p.val0()).unwrap_or(self.input.len());
        let hi = it.next().map(|p| p.val0()).unwrap_or(self.input.len());
        self.errors.push(Error {
            lo: lo,
            hi: hi,
            desc: match self.cur.clone().next() {
                Some((_, c)) => format!("expected `{}`, but found `{}`", ch, c),
                None => format!("expected `{}`, but found eof", ch)
            }
        });
        false
    }

    fn ws(&mut self) {
        loop {
            match self.cur.clone().next() {
                Some((_, '\t')) |
                Some((_, ' ')) => { self.cur.next(); }
                _ => break,
            }
        }
    }

    fn comment(&mut self) {
        match self.cur.clone().next() {
            Some((_, '#')) => {}
            _ => return,
        }
        for (_, ch) in self.cur {
            if ch == '\n' { break }
        }
    }

    pub fn parse(&mut self) -> Option<Table> {
        let mut ret = HashMap::new();
        loop {
            self.ws();
            match self.cur.clone().next() {
                Some((_, '#')) => { self.comment(); }
                Some((_, '\n')) => { self.cur.next(); }
                Some((start, '[')) => {
                    self.cur.next();
                    let array = self.eat('[');
                    let mut section = String::new();
                    for (pos, ch) in self.cur {
                        if ch == ']' { break }
                        if ch == '[' {
                            self.errors.push(Error {
                                lo: pos,
                                hi: pos + 1,
                                desc: format!("section names cannot contain \
                                               a `[` character"),
                            });
                            continue
                        }
                        section.push_char(ch);
                    }

                    if section.len() == 0 {
                        self.errors.push(Error {
                            lo: start,
                            hi: start + if array {3} else {1},
                            desc: format!("section name must not be empty"),
                        });
                        continue
                    } else if array && !self.expect(']') {
                        return None
                    }

                    let mut table = HashMap::new();
                    if !self.values(&mut table) { return None }
                    if array {
                        self.insert_array(&mut ret, section, Table(table), start)
                    } else {
                        self.insert_table(&mut ret, section, table, start)
                    }
                }
                Some(_) => {
                    if !self.values(&mut ret) { return None }
                }
                None if self.errors.len() == 0 => return Some(ret),
                None => return None,
            }
        }
    }

    fn values(&mut self, into: &mut Table) -> bool {
        loop {
            self.ws();
            match self.cur.clone().next() {
                Some((_, '#')) => self.comment(),
                Some((_, '\n')) => { self.cur.next(); }
                Some((_, '[')) => break,
                Some((start, _)) => {
                    let mut key = String::new();
                    let mut found_eq = false;
                    for (pos, ch) in self.cur {
                        match ch {
                            ' ' | '\t' => break,
                            '=' => { found_eq = true; break }
                            '\n' => {
                                self.errors.push(Error {
                                    lo: start,
                                    hi: pos + 1,
                                    desc: format!("keys cannot be defined \
                                                   across lines"),
                                })
                            }
                            c => key.push_char(c),
                        }
                    }
                    if !found_eq {
                        self.ws();
                        if !self.expect('=') { return false }
                    }

                    let value = match self.value() {
                        Some(value) => value,
                        None => return false,
                    };
                    self.insert(into, key, value, start);
                    self.ws();
                    self.comment();
                    self.eat('\n');
                }
                None => break,
            }
        }
        return true
    }

    fn value(&mut self) -> Option<Value> {
        self.ws();
        match self.cur.clone().next() {
            Some((pos, '"')) => self.string(pos),
            Some((pos, 't')) |
            Some((pos, 'f')) => self.boolean(pos),
            Some((pos, '[')) => self.array(pos),
            Some((pos, '-')) => self.number_or_datetime(pos),
            Some((pos, ch)) if ch.is_digit() => self.number_or_datetime(pos),
            _ => {
                let mut it = self.cur.clone();
                let lo = it.next().map(|p| p.val0()).unwrap_or(self.input.len());
                let hi = it.next().map(|p| p.val0()).unwrap_or(self.input.len());
                self.errors.push(Error {
                    lo: lo,
                    hi: hi,
                    desc: format!("expected a value"),
                });
                return None
            }
        }
    }

    fn string(&mut self, start: uint) -> Option<Value> {
        if !self.expect('"') { return None }
        let mut ret = String::new();

        loop {
            match self.cur.next() {
                Some((_, '"')) => break,
                Some((pos, '\\')) => {
                    match escape(self, pos) {
                        Some(c) => ret.push_char(c),
                        None => {}
                    }
                }
                Some((pos, ch)) if ch < '\u001f' => {
                    let mut escaped = String::new();
                    ch.escape_default(|c| escaped.push_char(c));
                    self.errors.push(Error {
                        lo: pos,
                        hi: pos + 1,
                        desc: format!("control character `{}` must be escaped",
                                      escaped)
                    });
                }
                Some((_, ch)) => ret.push_char(ch),
                None => {
                    self.errors.push(Error {
                        lo: start,
                        hi: self.input.len(),
                        desc: format!("unterminated string literal"),
                    });
                    return None
                }
            }
        }

        return Some(String(ret));

        fn escape(me: &mut Parser, pos: uint) -> Option<char> {
            match me.cur.next() {
                Some((_, 'b')) => Some('\u0008'),
                Some((_, 't')) => Some('\u0009'),
                Some((_, 'n')) => Some('\u000a'),
                Some((_, 'f')) => Some('\u000c'),
                Some((_, 'r')) => Some('\u000d'),
                Some((_, '"')) => Some('\u0022'),
                Some((_, '/')) => Some('\u002f'),
                Some((_, '\\')) => Some('\u005c'),
                Some((pos, 'u')) => {
                    let num = if me.input.is_char_boundary(pos + 5) {
                        me.input.slice(pos + 1, pos + 5)
                    } else {
                        "invalid"
                    };
                    match FromStrRadix::from_str_radix(num, 16) {
                        Some(n) => {
                            match char::from_u32(n) {
                                Some(c) => {
                                    me.cur.next();
                                    me.cur.next();
                                    me.cur.next();
                                    me.cur.next();
                                    return Some(c)
                                }
                                None => {
                                    me.errors.push(Error {
                                        lo: pos + 1,
                                        hi: pos + 5,
                                        desc: format!("codepoint `{:x}` is \
                                                       not a valid unicode \
                                                       codepoint", n),
                                    })
                                }
                            }
                        }
                        None => {
                            me.errors.push(Error {
                                lo: pos,
                                hi: pos + 1,
                                desc: format!("expected four hex digits \
                                               after a `u` escape"),
                            })
                        }
                    }
                    None
                }
                Some((pos, ch)) => {
                    let mut escaped = String::new();
                    ch.escape_default(|c| escaped.push_char(c));
                    let next_pos = me.next_pos();
                    me.errors.push(Error {
                        lo: pos,
                        hi: next_pos,
                        desc: format!("unknown string escape: `{}`",
                                      escaped),
                    });
                    None
                }
                None => {
                    me.errors.push(Error {
                        lo: pos,
                        hi: pos + 1,
                        desc: format!("unterminated escape sequence"),
                    });
                    None
                }
            }
        }
    }

    fn number_or_datetime(&mut self, start: uint) -> Option<Value> {
        let negative = self.eat('-');
        let mut is_float = false;
        loop {
            match self.cur.clone().next() {
                Some((_, ch)) if ch.is_digit() => { self.cur.next(); }
                Some((_, '.')) if !is_float => {
                    is_float = true;
                    self.cur.next();
                }
                Some(_) | None => break,
            }
        }
        let end = self.next_pos();
        let ret = if is_float {
            if self.input.char_at_reverse(end) == '.' {
                None
            } else {
                from_str::<f64>(self.input.slice(start, end)).map(Float)
            }
        } else if !negative && self.eat('-') {
            self.datetime(start, end + 1)
        } else {
            from_str::<i64>(self.input.slice(start, end)).map(Integer)
        };
        if ret.is_none() {
            self.errors.push(Error {
                lo: start,
                hi: end,
                desc: format!("invalid numeric literal"),
            });
        }
        return ret;
    }

    fn boolean(&mut self, start: uint) -> Option<Value> {
        let rest = self.input.slice_from(start);
        if rest.starts_with("true") {
            for _ in range(0, 4) {
                self.cur.next();
            }
            Some(Boolean(true))
        } else if rest.starts_with("false") {
            for _ in range(0, 5) {
                self.cur.next();
            }
            Some(Boolean(false))
        } else {
            let next = self.next_pos();
            self.errors.push(Error {
                lo: start,
                hi: next,
                desc: format!("unexpected character: `{}`",
                             rest.char_at(0)),
            });
            None
        }
    }

    fn datetime(&mut self, start: uint, end_so_far: uint) -> Option<Value> {
        let mut date = self.input.slice(start, end_so_far).to_string();
        for _ in range(0, 15) {
            match self.cur.next() {
                Some((_, ch)) => date.push_char(ch),
                None => {
                    self.errors.push(Error {
                        lo: start,
                        hi: end_so_far,
                        desc: format!("malformed date literal"),
                    });
                    return None
                }
            }
        }
        let mut it = date.as_slice().chars();
        let mut valid = true;
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == '-').unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == '-').unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == 'T').unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == ':').unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == ':').unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c.is_digit()).unwrap_or(false);
        valid = valid && it.next().map(|c| c == 'Z').unwrap_or(false);
        if valid {
            Some(Datetime(date.clone()))
        } else {
            self.errors.push(Error {
                lo: start,
                hi: start + date.len(),
                desc: format!("malformed date literal"),
            });
            None
        }
    }

    fn array(&mut self, _start: uint) -> Option<Value> {
        if !self.expect('[') { return None }
        let mut ret = Vec::new();
        fn consume(me: &mut Parser) {
            loop {
                me.ws();
                match me.cur.clone().next() {
                    Some((_, '#')) => { me.comment(); }
                    Some((_, '\n')) => { me.cur.next(); }
                    _ => break,
                }
            }
        }
        let mut type_str = None;
        loop {
            // Break out early if we see the closing bracket
            consume(self);
            if self.eat(']') { return Some(Array(ret)) }

            // Attempt to parse a value, triggering an error if it's the wrong
            // type.
            let start = self.next_pos();
            let value = match self.value() {
                Some(v) => v,
                None => return None,
            };
            let end = self.next_pos();
            let expected = type_str.unwrap_or(value.type_str());
            if value.type_str() != expected {
                self.errors.push(Error {
                    lo: start,
                    hi: end,
                    desc: format!("expected type `{}`, found type `{}`",
                                  expected, value.type_str()),
                });
            } else {
                type_str = Some(expected);
                ret.push(value);
            }

            // Look for a comma. If we don't find one we're done
            consume(self);
            if !self.eat(',') { break }
        }
        consume(self);
        if !self.expect(']') { return None }
        return Some(Array(ret))
    }

    fn insert(&mut self, into: &mut Table, key: String, value: Value,
              key_lo: uint) {
        if into.contains_key(&key) {
            self.errors.push(Error {
                lo: key_lo,
                hi: key_lo + key.len(),
                desc: format!("duplicate key: `{}`", key),
            })
        } else {
            into.insert(key, value);
        }
    }

    fn recurse<'a>(&mut self, mut cur: &'a mut Table, orig_key: &'a str,
                   key_lo: uint) -> Option<(&'a mut Table, &'a str)> {
        if orig_key.starts_with(".") || orig_key.ends_with(".") ||
           orig_key.contains("..") {
            self.errors.push(Error {
                lo: key_lo,
                hi: key_lo + orig_key.len(),
                desc: format!("tables cannot have empty names"),
            });
            return None
        }
        let key = match orig_key.rfind('.') {
            Some(n) => orig_key.slice_to(n),
            None => return Some((cur, orig_key)),
        };
        for part in key.as_slice().split('.') {
            let part = part.to_string();
            let tmp = cur;

            if tmp.contains_key(&part) {
                match *tmp.get_mut(&part) {
                    Table(ref mut table) => {
                        cur = table;
                        continue
                    }
                    Array(ref mut array) => {
                        match array.as_mut_slice().mut_last() {
                            Some(&Table(ref mut table)) => cur = table,
                            _ => {
                                self.errors.push(Error {
                                    lo: key_lo,
                                    hi: key_lo + key.len(),
                                    desc: format!("array `{}` does not contain \
                                                   tables", part)
                                });
                                return None
                            }
                        }
                        continue
                    }
                    _ => {
                        self.errors.push(Error {
                            lo: key_lo,
                            hi: key_lo + key.len(),
                            desc: format!("key `{}` was not previously a table",
                                          part)
                        });
                        return None
                    }
                }
            }

            // Initialize an empty table as part of this sub-key
            tmp.insert(part.clone(), Table(HashMap::new()));
            match *tmp.get_mut(&part) {
                Table(ref mut inner) => cur = inner,
                _ => unreachable!(),
            }
        }
        return Some((cur, orig_key.slice_from(key.len() + 1)))
    }

    fn insert_table(&mut self, into: &mut Table, key: String, value: Table,
                    key_lo: uint) {
        if !self.tables_defined.insert(key.clone()) {
            self.errors.push(Error {
                lo: key_lo,
                hi: key_lo + key.len(),
                desc: format!("redefinition of table `{}`", key),
            });
            return
        }

        let (into, key) = match self.recurse(into, key.as_slice(), key_lo) {
            Some(pair) => pair,
            None => return,
        };
        let key = key.to_string();
        if !into.contains_key(&key) {
            into.insert(key.clone(), Table(HashMap::new()));
        }
        match into.find_mut(&key) {
            Some(&Table(ref mut table)) => {
                for (k, v) in value.move_iter() {
                    if !table.insert(k.clone(), v) {
                        self.errors.push(Error {
                            lo: key_lo,
                            hi: key_lo + key.len(),
                            desc: format!("duplicate key `{}` in table", k),
                        });
                    }
                }
            }
            Some(_) => {
                self.errors.push(Error {
                    lo: key_lo,
                    hi: key_lo + key.len(),
                    desc: format!("duplicate key `{}` in table", key),
                });
            }
            None => {}
        }
    }

    fn insert_array(&mut self, into: &mut Table, key: String, value: Value,
                   key_lo: uint) {
        let (into, key) = match self.recurse(into, key.as_slice(), key_lo) {
            Some(pair) => pair,
            None => return,
        };
        let key = key.to_string();
        if !into.contains_key(&key) {
            into.insert(key.clone(), Array(Vec::new()));
        }
        match *into.get_mut(&key) {
            Array(ref mut vec) => {
                match vec.as_slice().head() {
                    Some(ref v) if !v.same_type(&value) => {
                        self.errors.push(Error {
                            lo: key_lo,
                            hi: key_lo + key.len(),
                            desc: format!("expected type `{}`, found type `{}`",
                                          v.type_str(), value.type_str()),
                        })
                    }
                    Some(..) | None => {}
                }
                vec.push(value);
            }
            _ => {
                self.errors.push(Error {
                    lo: key_lo,
                    hi: key_lo + key.len(),
                    desc: format!("key `{}` was previously not an array", key),
                });
            }
        }
    }
}