use language::BufferSnapshot;
use std::{fmt::Write, ops::Range};

pub fn generate_content_prompt(
    user_prompt: String,
    language_name: Option<&str>,
    buffer: BufferSnapshot,
    range: Range<usize>,
    project_name: Option<String>,
) -> anyhow::Result<String> {
    let mut prompt = String::new();

    let content_type = match language_name {
        None | Some("Markdown" | "Plain Text") => {
            writeln!(prompt, "You are an expert engineer.")?;
            "Text"
        }
        Some(language_name) => {
            writeln!(prompt, "You are an expert {language_name} engineer.")?;
            writeln!(
                prompt,
                "Your answer MUST always and only be valid {}.",
                language_name
            )?;
            "Code"
        }
    };

    if let Some(project_name) = project_name {
        writeln!(
            prompt,
            "You are currently working inside the '{project_name}' project in code editor Zed."
        )?;
    }

    // Include file content.
    for chunk in buffer.text_for_range(0..range.start) {
        prompt.push_str(chunk);
    }

    if range.is_empty() {
        prompt.push_str("<|START|>");
    } else {
        prompt.push_str("<|START|");
    }

    for chunk in buffer.text_for_range(range.clone()) {
        prompt.push_str(chunk);
    }

    if !range.is_empty() {
        prompt.push_str("|END|>");
    }

    for chunk in buffer.text_for_range(range.end..buffer.len()) {
        prompt.push_str(chunk);
    }

    prompt.push('\n');

    if range.is_empty() {
        writeln!(
            prompt,
            "Assume the cursor is located where the `<|START|>` span is."
        )
        .unwrap();
        writeln!(
            prompt,
            "{content_type} can't be replaced, so assume your answer will be inserted at the cursor.",
        )
        .unwrap();
        writeln!(
            prompt,
            "Generate {content_type} based on the users prompt: {user_prompt}",
        )
        .unwrap();
    } else {
        writeln!(prompt, "Modify the user's selected {content_type} based upon the users prompt: '{user_prompt}'").unwrap();
        writeln!(prompt, "You must reply with only the adjusted {content_type} (within the '<|START|' and '|END|>' spans) not the entire file.").unwrap();
        writeln!(
            prompt,
            "Double check that you only return code and not the '<|START|' and '|END|'> spans"
        )
        .unwrap();
    }

    writeln!(prompt, "Never make remarks about the output.").unwrap();
    writeln!(
        prompt,
        "Do not return anything else, except the generated {content_type}."
    )
    .unwrap();

    Ok(prompt)
}