use std::panic;

use diff_match_patch_rs::{Compat, DiffMatchPatch, PatchInput};
use reconcile_text::{BuiltinTokenizer, reconcile};

fn dmp_merge(parent: &str, left: &str, right: &str) -> Option<String> {
    let parent = parent.to_owned();
    let left = left.to_owned();
    let right = right.to_owned();

    // diff-match-patch-rs can panic on some inputs, so we catch that.
    panic::catch_unwind(|| {
        let dmp = DiffMatchPatch::new();
        let diffs = dmp.diff_main::<Compat>(&parent, &left).ok()?;
        let patches = dmp
            .patch_make(PatchInput::new_text_diffs(&parent, &diffs))
            .ok()?;
        let (result, _) = dmp.patch_apply(&patches, &right).ok()?;
        Some(result)
    })
    .ok()
    .flatten()
}

fn try_merge(parent: &str, left: &str, right: &str) {
    let dmp_result = dmp_merge(parent, left, right);

    let reconcile_result = reconcile(
        parent,
        &left.into(),
        &right.into(),
        &*BuiltinTokenizer::Word,
    )
    .apply()
    .text();

    println!("Parent: {parent:?}");
    println!("Left:   {left:?}");
    println!("Right:  {right:?}");
    println!();
    match dmp_result {
        Some(r) => println!("diff-match-patch: {r:?}"),
        None => println!("diff-match-patch: <panic or error>"),
    }
    println!("reconcile-text:   {reconcile_result:?}");
    println!();
}

/// Demonstrates cases where diff-match-patch silently produces incorrect
/// output, while reconcile-text preserves both users' edits correctly
///
/// Run it with:
/// `cargo run --example compare-with-diff-match-patch`
fn main() {
    // Example 1
    // Two users edit the same short phrase. Alice replaces "old(!)" with
    // "new improved", Bob replaces "broken" with "working". These are
    // independent changes to adjacent words.
    //
    // diff-match-patch has no common ancestor, so it diffs parent → left
    // and applies the patch to right. The character-level patches overlap
    // and produce garbled text ("impovind"). It reports success.
    //
    // reconcile-text sees both changes relative to the parent and merges
    // them cleanly.

    println!("── Example 1: adjacent edits ──");
    try_merge(
        "old(!) broken code",
        "new improved code",
        "old(!) working code",
    );

    // Example 2
    // Alice adds a sentence. Bob rewrites the surrounding text. Because
    // diff-match-patch works without a common ancestor, Alice's entire
    // sentence is silently lost.

    println!("── Example 2: sentence lost ──");
    // Alice adds a sentence in the middle of a paragraph. Bob rephrases
    // the same paragraph. Because the patch context from Alice's edit no
    // longer appears in Bob's version, diff-match-patch silently drops
    // Alice's entire sentence.
    //
    // reconcile-text understands both edits relative to the common ancestor
    // and keeps both.
    try_merge(
        "We used the existing parsing approach for processing. The output was saved to the \
         database.",
        "We used the existing parsing approach for processing. Always validate the schema! The \
         output was saved to the database.",
        "We adopted a brand new analysis pipeline for execution. The results were written to \
         cloud storage.",
    );
}