use regex::Regex;
use std::{collections::HashSet, env, error::Error, fs, path::Path, process::Command};

fn escape_template(v: &str) -> Result<String, String> {
    let cant_escape = "\\{";
    if v.contains(cant_escape) {
        return Err(format!("can't escape {cant_escape}"));
    }
    Ok(v.replace("{", "\\{"))
}

fn main() -> Result<(), Box<dyn Error>> {
    println!("cargo:rerun-if-changed=migrations");
    println!("cargo:rerun-if-changed=website");
    let out_dir = env::var_os("OUT_DIR").unwrap();
    let website_dir = Path::new(&out_dir).join("website");
    let templates_dir = Path::new(&out_dir).join("templates");
    fs::create_dir_all(&templates_dir)?;
    let status = Command::new("mdbook")
        .arg("build")
        .arg("--dest-dir")
        .arg(&website_dir)
        .current_dir("website")
        .status()
        .map_err(|e| format!("Can't run mdbook: {e}"))?;
    if !status.success() {
        return Err(format!("mdbook exited with an error: {status:?}").into());
    }
    let sub_template_path = website_dir.join("subscription/index.html");
    let sub_template = fs::read_to_string(&sub_template_path)
        .map_err(|e| format!("Error reading {}: {e}", sub_template_path.display()))?;
    let regex = Regex::new(r#"(?s)<div class="subscribe_list_template_section" id="(?<id>[^"]*)"/>(?<template>.*?)<div class="subscribe_list_template_section"/>"#).unwrap();
    let matches = Vec::from_iter(regex.captures_iter(&sub_template));
    let mut between_matches = vec![];
    let mut last_end = 0;
    for m in &matches {
        let m = m.get(0).unwrap();
        between_matches.push(&sub_template[last_end..m.start()]);
        last_end = m.end();
    }
    between_matches.push(&sub_template[last_end..]);
    let prefix = between_matches.remove(0);
    let Some(suffix) = between_matches.pop() else {
        return Err(format!(
            "no subscribe_list_template_section `div`s found: {}",
            sub_template_path.display()
        )
        .into());
    };
    let prefix = escape_template(prefix)?;
    let suffix = escape_template(suffix)?;
    for i in between_matches {
        if i.trim_start() != "" {
            return Err(format!(
                r#"can't have non-whitespace text between
<div class="subscribe_list_template_section"/>
and next
<div class="subscribe_list_template_section" id="..">"#
            )
            .into());
        }
    }
    let mut identifiers = HashSet::new();
    for m in &matches {
        let id = &m["id"];
        if id.contains(|ch: char| !ch.is_ascii_alphanumeric() && ch != '_') {
            return Err(format!("invalid identifier {id:?}").into());
        }
        if !identifiers.insert(id) {
            return Err(format!("duplicate identifier {id:?}").into());
        }
        let template = &m["template"];
        fs::write(
            templates_dir.join(format!("{id}.txt")),
            prefix.clone() + template + &suffix,
        )?;
    }
    Ok(())
}