use std::cell::Cell;
use std::fmt;
use std::fs::metadata;
use std::time::SystemTime;

use eyre::{Result, WrapErr};

use crate::makefile::command_line::CommandLine;

use super::Makefile;

#[derive(PartialEq, Eq, Clone, Debug)]
pub struct Target {
    pub name: String,
    pub prerequisites: Vec<String>,
    pub commands: Vec<CommandLine>,
    pub already_updated: Cell<bool>,
}

impl Target {
    fn modified_time(&self) -> Option<SystemTime> {
        metadata(&self.name)
            .and_then(|metadata| metadata.modified())
            .ok()
    }

    pub fn newer_than(&self, other: &Self) -> Option<bool> {
        let self_updated = self.already_updated.get();
        let other_updated = other.already_updated.get();
        Some(match (self.modified_time(), other.modified_time()) {
            (Some(self_mtime), Some(other_mtime)) => self_mtime >= other_mtime,
            // per POSIX: "If the target does not exist after the target has been
            // successfully made up-to-date, the target shall be treated as being
            // newer than any target for which it is a prerequisite."
            (None, _) if self_updated && other.prerequisites.contains(&self.name) => true,
            (_, None) if other_updated && self.prerequisites.contains(&other.name) => false,
            _ => return None,
        })
    }

    fn is_up_to_date(&self, file: &Makefile) -> bool {
        if self.already_updated.get() {
            return true;
        }
        #[cfg(feature = "full")]
        if file.special_target_has_prereq(".PHONY", &self.name) {
            return false;
        }
        let exists = metadata(&self.name).is_ok();
        let newer_than_all_dependencies = self.prerequisites.iter().all(|t| {
            file.get_target(t)
                .ok()
                .and_then(|t| self.newer_than(&t.borrow()))
                .unwrap_or(false)
        });
        exists && newer_than_all_dependencies
    }

    pub fn update(&self, file: &Makefile) -> Result<()> {
        for prereq in &self.prerequisites {
            file.update_target(prereq)
                .wrap_err_with(|| format!("as a dependency for target {}", self.name))?;
        }
        if !self.is_up_to_date(file) {
            self.execute_commands(file)
                .wrap_err_with(|| format!("while updating target {}", self.name))?;
        }
        self.already_updated.set(true);

        Ok(())
    }

    fn execute_commands(&self, file: &Makefile) -> Result<()> {
        for command in &self.commands {
            command.execute(file, self)?;
        }

        Ok(())
    }
}

impl fmt::Display for Target {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let prereqs = self.prerequisites.join(" ");
        writeln!(f, "{}: {}", &self.name, prereqs)?;
        for command in &self.commands {
            writeln!(f, "\t{}", command)?;
        }
        Ok(())
    }
}